use constant for total so that it will be converted to bit shift by compiler

git-svn-id: http://svn.coderepos.org/share/lang/cplusplus/range_coder@7161 d0d07461-0603-4401-acd4-de1884942a52

Author: kazuho

bench.cpp

@@ -51,8 +51,7 @@ int main(int argc, char **argv)
       ch = to_ordered[ch];
 #endif
       assert(freq[ch] != freq[ch + 1]);
-      enc.encode(freq[ch] - FREQ_BASE, freq[ch + 1] - FREQ_BASE,
-		 freq[256] - FREQ_BASE);
+      enc.encode(freq[ch] - FREQ_BASE, freq[ch + 1] - FREQ_BASE, MAX_FREQ);
     }
     enc.final();
     cbuflen = cbufpt - cbuf;
@@ -64,7 +63,7 @@ int main(int argc, char **argv)
     rc_decoder_t<const char*, rc_decoder_search_t<short, 256, FREQ_BASE> >
       dec(cbuf, cbuf + cbuflen);
     for (char *p = rbuf, *e = rbuf + buflen; p != e; p++) {
-      unsigned ch = dec.decode(freq[256] - FREQ_BASE, freq);
+      unsigned ch = dec.decode(MAX_FREQ, freq);
 #ifdef USE_ORDERED_TABLE
       ch = from_ordered[ch];
 #endif

build_table.pl

@@ -4,7 +4,7 @@
 use warnings;
 
 use Getopt::Long;
-use List::Util qw/sum/;
+use List::Util qw/sum max/;
 
 my ($do_ordered);
 
@@ -33,10 +33,22 @@
 my @freq;
 my $acc = 0;
 my $cc = sum @cnt;
-for (my $i = 0; $i < 256; $i++) {
-    push @freq, $acc;
-    $acc += int(($cnt[$i] / $cc) * 0xfe00);
+my ($mult, $mult_diff) = (0x8000, 0);
+while (1) {
+    $acc = 0;
+    for (my $i = 0; $i < 256; $i++) {
+	push @freq, $acc;
+	$acc += $cnt[$i] != 0 ? max(int($cnt[$i] / $cc * $mult + 0.5), 1) : 0;
+    }
+    last if $acc == 0x8000;
+    @freq = ();
+    $mult_diff = $mult_diff != 0 ? $mult_diff / 2 : abs($acc - 0x8000);
+    if ($acc < 0x8000) {
+	$mult += $mult_diff;
+    } else {
+	$mult -= $mult_diff;
+    }
 }
-push @freq, $acc;
 
+print "#define MAX_FREQ 0x8000\n";
 print "static short freq[] __attribute__((aligned(16))) = {", join(',', map { $_ - 0x8000 } @freq), "};\n";